Comparison of endothelial function and sensory thermal thresholds in cold sensitive and control individuals

Individuals who have low peripheral skin temperatures in a warm environment and a slow rate of rewarming following a local cold stimulus are considered to be cold sensitive (CS). Therefore, CS may represent a subclinical non-freezing cold injury. The mechanisms underpinning CS have not been determined, therefore this study compared endothelialfunction and thresholds for warm and cold sensation in individuals with CS to matched controls.

Nine participants (5 men) with CS and nine control participants (5 men) undertook a CS test of the foot involving cooling in 15 °C water for 2 minutes with spontaneous rewarming in 30 °C air. Endothelial function was assessed at the forearm, finger and foot by iontophoresis of 1% w/w acetylcholine. Cutaneous vascular conductance (CVC) was calculated from laser Doppler flux and corrected for mean arterial pressure. Sensory thermal thresholds to heating and cooling of the fingers and foot were also determined.

There was no difference between groups for age, height, mass, BMI, skinfold thickness, foot volume or physical activity. Compared to the control group, mean [SD] toe skin temperature was significantly lower in the CS group prior to immersion (30.3 [0.9] °C v 34.8 [0.8] °C; P<0.001) and after 5 min of rewarming (27.9 [0.8] °C v 34.3 [0.9] °C; P<0.001). This was associated with a reduced CVC in the Great toe in the CS group (pre: 1.08 [0.79] flux.mmHg^-1v 3.83 [1.21] flux.mmHg^-1; 5 min: 0.79 [0.52] flux.mmHg^-1v 3.46 [1.07] flux.mmHg^-1P<0.001). The CS group had a lower sensory threshold to cold stimuli in their feet compared to controls (median [interquartile range]: 0.3 [0.4 –0.7] °C v 0.5 [0.4 –0.7] °C; P=0.05). Warm sensory thresholds in the feet and cold and warm sensory thresholds in the fingers were similar between groups. No differences in the responses to acetylcholine in the forearm, finger or foot were observed between groups.

Although CS individuals had lower toe CVC and temperatures in a warm environment and rewarmed more slowly following brief cold exposure of the foot, their endothelium-dependent vasodilation was comparable to that of controls. CS individuals were able to perceive smaller changes in foot skin temperature during cooling than controls, although the numerical difference between the groups was small. This indicates that the sensory cues for behavioural responses to the cold are unlikely to be compromised. Further research, possibly focusing on vasoconstrictor pathways, is required to understand the mechanisms involved in CS.